[linux-lvm] read only filesystem on LVM device after changing path in SAN

From: Sebastian Reitenbach <sebastia l00-bugdead-prods de>

To: linux-lvm redhat com

Subject: [linux-lvm] read only filesystem on LVM device after changing path in SAN

Date: Mon, 8 Jun 2009 17:48:01 +0200

Hi,
I hope I am right here, if not, please let me know where would be a better
place to ask. I have observed a problem on LVM based partitions when I change
the paths through the SAN.
Here my setup: I have a 3TB partition, coming from a SAN IBM DS4700, the same
but smaller, for the operating system partition. Both presented to a xen
host. On the data partition I have a LVM configured. There are four paths
through the SAN for each of the disks. The host type on the DS4700 for the
server is configured as LNXCLVMWARE, which as for the documentation should be
the right one.
# multipath -ll
Pilot-Project-VMs (3600a0b800048b31000000ffd4a10fd7e) dm-1 IBM,1814 FAStT
[size=280G][features=1 queue_if_no_path][hwhandler=1 rdac][rw]
\_ round-robin 0 [prio=2][enabled]
\_ 4:0:1:0 sdf 8:80 [active][ghost]
\_ 3:0:1:0 sdg 8:96 [active][ghost]
\_ round-robin 0 [prio=12][active]
\_ 3:0:0:0 sdb 8:16 [active][ready]
\_ 4:0:0:0 sdc 8:32 [active][ready]
Pilot-Project-Data (3600a0b800048b31000000fbe49f962e5) dm-3 IBM,1814
FAStT
[size=3.0T][features=1 queue_if_no_path][hwhandler=1 rdac][rw]
\_ round-robin 0 [prio=2][enabled]
\_ 4:0:1:1 sdh 8:112 [active][ghost]
\_ 3:0:1:1 sdi 8:128 [active][ghost]
\_ round-robin 0 [prio=12][enabled]
\_ 3:0:0:1 sdd 8:48 [active][ready]
\_ 4:0:0:1 sde 8:64 [active][ready]
When I run a dd copy job, creating a file on the Operating system partition,
e.g. dd if=7dev/zero of=/data/file then everything seems to be fine. I change
the path through the SAN via the DS4700 management GUI, and the dd job keeps
running as expected, so no problem without LVM.
When I do the same on the LVM partition, then after some seconds, after I
switch the preferred path through the SAN, then the LVM partiton becomes
read-only, and the dd job dies. Then on the dom0, a
fdisk -l /dev/mapper/3TB-Partion still shows output, but
fdisk -l /dev/mapper/3TB--Partion-1 on the LVM device, just shows nothing.
When I then shutdown the xen host, and do a:
/etc/init.d/boot.lvm restart
then fdisk -l /dev/mapper/3TB--Partion-1 on the LVM device, produces output
again. However, the startup of the xen domU may still spit out errors, and
the mounting of the device in the domU may still not work. I had to reboot
the dom0 physical host to get the partition back in a working state.
I do not have any kind of special configuration for the LVM device, I created
it via yast2.
Is there anything what I can do to prevent the LVM based partition to become
read-only when a path in the SAN switches?
If I need to provide more information let me know whats needed.
kind regards
Sebastian